In recent years, for less attention paid, the rotary sealing technologies for large-scale rotary equipment are not developed hugely. In known rotary sealing technologies, it is quite difficult for a mixing drum to meet requirements of rotary sealing of its port in rotating state in bad working conditions.
A few of reports mention a mixing-and-transport truck on which a mixing drum is installed horizontally. The feed-in port of the mixing-and-transport truck rotates together with the mixing drum. However, the mixing drum cannot be rotated when feeding materials and the concrete cannot be stirred continuously and accordingly the quality of the concrete cannot be guaranteed. In addition, as the mixing drum cannot be rotated when feeding materials, the concrete will be accumulated near the feed-in port which results in the failure of active feeding.
From prior arts, it cannot lead to rotary sealing of the port for a mixing drum in rotary state. The mixing drums on mixing-and-transport trucks used broadly in the world are still laid in a tilted position at large inclination angles (for example, 15 degree inclination angle). However, there exist the following deficiencies in the prior arts:                1) The tilted position at a large inclination angle causes higher center of gravity. Thus it will increase the risk of overturn accidents due to the unsafe and difficult driving. In fact, the traffic accidents of this kind of vehicles are recurring frequently. Large numbers of reports involved that are published each year.        2) The tilted position at a large inclination angle causes stratification of the concrete in the mixing drum, which will be growing worse as time goes by. The concrete discharged will be heterogeneous and thus the concrete will be stratified when depositing.        3) The fact that the tilted position at a large inclination angle causes higher center of gravity brings about the failure of providing a heating device and because of this, the mixing drum will keep operating in open-air circumstances and the heat will not be retained well. Especially in summers and winters, the concrete is always found disqualified as the temperature cannot meet the required standard.        4) Because the known mixing drum is in open state and no heating device is provided, the phenomenon of “stir-frying cauldron” will be produced where the mixing drum is rotating with heat conduction in the sun shine, and the water in the concrete may be evaporated rapidly. Therefore, when depositing the concrete, the water is required to be supplied again. It will lead to the deteriorated quality and even lost effectiveness of concrete. Therefore, it will be severely restricted not only for the effective time in the mixing drum but also the transportation distance.        5) Because the known mixing drum is in open state, it is easy for hot or cold air, snow or rain to interfuse into the mixing drum, by which the concrete quality will be reduced sharply.        6) Finally, the structure of this equipment grows increasingly obsolete and low automatic.        